Slick 60's

Need an automatic gearbox instead of my three on a tree. 390 in a 250 is not good for my wallet. Need an overdrive real baaad.Witch one can stand the power of an 390.

just an opinion but i think you might be better off getting a different rear end ratio. f250s are usually pretty tall, 4.10 or 4.56 depending what you are using the truck for you might want to go to 3.50 or even 3.25 if you are not hauling much weight.

Yep, if you have a F250 the ratio is the problem, not your engine or trans. You're going to turn too many rpms with anything 4:00 or higher numerical. I also don't know of any AOD trans that will bolt to a FE. Your only choice other than the FOM is the C6, which is not known for it's efficiency and is a lot heavier than what you've got in there as well.

I would make this decision on the type of use your using it for, if your city driving them 4.10s would be much better gearing or even 4.30s if your on the highway al lthe time and not hauling anything you will be better off using 3.50s or even higher 3.23s or whatever. if you go to an auto and your hauling your mileage will definately drop. might be better off with a Beefy 4 speed, Depending on the useage. I need 4.10s for my 06 damn 3.73s dont do it for city driving, Hell might even try for 4.30s if I can find a set for both axles for 5 bucks BC thats all I have